Subtropical Storm LESLIE

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Subtropical Storm Leslie Discussion Number 6
NWS National Hurricane Center Miami FL AL132018
500 PM AST Mon Sep 24 2018
Leslie's cloud pattern has become rather ragged and less organized
this afternoon. Visible satellite imagery indicates that the
surface circulation has become elongated, from north to south, with
multiple cloud swirls rotating within the larger gyre. The initial
intensity is held at 35 kt for this advisory and could be generous,
based on the earlier partial ASCAT-A wind retrievals. The
intensity forecast philosophy remains the same. Leslie is expected
to interact with the incoming baroclinic zone approaching from the
northwest and begin intensifying as it completes a
post-tropical/extratropical transition by mid period. The official
forecast is based on the IVCN multi-model intensity consensus
through 36 hours, and a blend of the global models after Leslie
becomes an extratropical low.
Based on a centroid position of the aforementioned multiple surface
swirls, Leslie continues to move in an eastward fashion, or 090/6
kt. Leslie should turn toward the east-northeast in 36 hours in
response to an approaching mid-latitude trough and associated cold
front from the northwest over the central Atlantic. The large-scale
models are in good agreement with Leslie completing an extratropical
transition at that time. Afterward, the post-tropical cyclone is
forecast to become cut off from the mid- to upper-tropospheric
westerly steering flow and move cyclonically toward the end of the
week between the building Bermuda high to the west and mid-level
ridging over the east Atlantic. The NHC forecast now shows Leslie
as a strengthening extratropical low through day 5, in agreement
with GFS, Canadian, and European models. Subsequently, the wind
radii forecast has also been adjusted based on a compromise of the
aforementioned large-scale models.
FORECAST POSITIONS AND MAX WINDS
INIT 24/2100Z 33.0N 47.2W 35 KT 40 MPH
12H 25/0600Z 32.9N 46.2W 35 KT 40 MPH
24H 25/1800Z 32.6N 44.0W 45 KT 50 MPH
36H 26/0600Z 33.4N 41.3W 50 KT 60 MPH...POST-TROP/EXTRATROP
48H 26/1800Z 35.4N 39.9W 55 KT 65 MPH...POST-TROP/EXTRATROP
72H 27/1800Z 36.9N 42.5W 50 KT 60 MPH...POST-TROP/EXTRATROP
96H 28/1800Z 36.7N 46.5W 50 KT 60 MPH...POST-TROP/EXTRATROP
120H 29/1800Z 36.2N 48.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
$$
Forecaster Roberts
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